Apparatus for freeze-drying and method



Nov. 23, 1965 v. w. LIND APPARATUS FOR FREEZE-DRYING AND METHOD 2 Sheets-Sheet l Filed July 17, 1962 Nov. 23, 1965 v. w. LIND 3,218,727

APPARATUS FOR FREEZE-DRYING AND METHOD Filed July 17, 1962 2 Sheets-Sheet 2 F/G 3 I9 24 25 S mf f EL INVENTOR. V/CTOR M4 L/ND 3,218,727 APPARATUS FOR FREEZE-DRYING AND METHOD Victor W. Lind, San Francisco, Calif.; Dorothy C. Lind, administratrix of said Victor W. Lind, deceased Filed July 17, 1962, Ser. No. 210,385 4 Claims. (Cl. 34-5) This invention relates to what is knovm as a freezedry system. A freeze-dry system is one in which products are frozen, so that the moisture in them is converted into complete ice crystallization. On complete crystallization these ice crystals are sublimated, leaving a dehydrated product.

By the apparatus and method heretofore employed, a long conveyor carrying the product to be dehydrated passes through a freezing chamber, in which chamber the freezing occurs. The product may be discrete bodies, such as vegetables, fruit, etc. By the conventional method, the essential step of complete crystallization of the moisture is relatively slow. The product is then moved through a vacuum chamber for vaporizing the ice crystals and withdrawing the vapors, which, heretofore, is another time consuming operation.

One of the objects of the present invention is the provision of apparatus, and a method, for freeze-drying a product within a small fraction of the time heretofore required, and which apparatus occupies a relatively small fraction of the floor space heretofore required by apparatus having a corresponding capacity.

An additional object of the invention is the provision of apparatus and a method of dehydrating food products that are more ecient and economical than heretofore.

Other objects and advantages will appear inthe description and drawings.

In the drawings, FIG. 1 is a semischematic plan view of apparatus adapted to accomplish the dehydration of products by my method.

FIG. 2 is a semischematic side elevational view of the apparatus for practicing the method of the present invention.

FIG. 3 is a slightly enlarged cross sectional view taken along line 3 3 of FIG. 1.

FIG. 4 is an enlarged part sectional and part elevational view of a portion of the apparatus, broken in length, but taken substantially along line 4-4 of FIG. 1.

FIG. 5 is an enlarged fragmentary view showing the lower portion of the conveyor between the freezing and drying rooms.

Referring to FIGS. 1, 2 a freezing room is generally designated 1 and a sublimation room is generally designated 2. Rooms 1 and 2 are each fully enclosed by walls, the walls of room 1 being insulated in the usual manner against transfer of heat, one Wall 3 of which is a partition wall between rooms 1 and 2, thereby being common to both rooms 1 and 2.

Within room 1 is a pair of conventional water defrosted, direct expansion air handling units 4 and 5 each including the usual cooling coils and respectively connected by fluid lines 6, 7, 8 and 9 with compressor and condenser units 10, 11 that are outside the room 1, while drain lines 12, 13 extend from the water collecting basins in the lower portion of each of the units 4, 5 to outside the room 1. Freezing of Water in the drain lines is prevented by the usual lead cable heating means to ensure drainage. Water lines 14, 15 extend to the customary water sprays within each unit 4, 5 for spraying the coils during the defrosting period.

The air cooling units 4, 5 are identical in structure, and may be positioned in spaced opposed relation spaced at opposite sides of a central plenum chamber 18. A

3,218,727 Patented Nov. 23, 1965 ICE conventional power drive in the upper portion of cooling unit 4 discharges the cold air through a side opening in the unit through a horizontally extending duct 19 into the plenum chamber 18, while air from the cooling unit 5 is adapted to be delivered through a similar duct 20 into said plenum chamber 18.

Conventional louver type dampers 22, 23 respectively in ducts 19, 20 are connected with electric -motors 24, 25, which, in turn, are in an electrical circuit with a motor driven timer switch 26 for automatically opening and closing said dampers for predetermined periods of time according to the setting of the timer.

It should be noted that the spray lines 14, 15 have solenoid actuated valves 27, 28 therein also in the electrical circuit with the timer switch 26 for actuation substantially simultaneously with actuation of the damper motors, as will later be described more in detail.

Connected with the plenum chamber 18 are three corresponding cold airI ducts 30, 31, and 32 in a vertical row (FIG. 2) which ducts extend horizontally from the same side of the plenum chamber 18, the duct 30 being uppermost and duct 32 lowermost.

At this point it may be noted that the air that is discharged from the ducts 30, 31, 32 as will later be described, is preferably at a temperature of from approximately 15 F. to approximately 30 F.; preferably the latter.

Within the freezing room 1 are a plurality of vertically spaced, horizontally elongated endless conveyor belts 33, 34 and 35 in superposed relation, with the conveyor 33 being indicated as the uppermost conveyor, while conveyor 35 is the lowermost.

The rooms 1, 2 are horizontally elongated. The invention is not to be considered as limited to any particular dimensions, but in an actual installation, as one example, rooms 1, 2 may each be approximately 36 feet in length and approximately 16 feet in height, with each conveyor 7-9 being approximately 30 feet in length, making a total of approximately feet of travel of material within room 1, or within a room length of approximately 36 feet.

Conveyors 33, 34 and 35 each extend at their ends over conventional rollers on pulleys the shafts of which are journalled for rotation in conventional bearings that may be supported on suitable frame members (not shown) within room 1. The right hand end wall 36 of room 1, as seen in FIG. 2, or the end wall that is opposite to the partition wall 3, is formed withan opening adjacent to the upper end of said wall through which extends the discharge end of a conventional, horizontally extending, endless feed conveyor 37. The roller or pulley support- ,ing the discharge end of said feed conveyor Within the upper portion of room 1 adjacent to end wall 36 has its supporting shaft suitably supported for rotation within said upper end of room 1.

The conveyors 33, 34 and 35 may be of any suitable belting material, but each preferably is of anti-sticking material, such as the plastic known to the trade under the trade name .of Teflon. Such material is hard, inextensible, extremely strong, and is resistant to adhesion of the products adapted to be supported thereon, and will withstand, without change, variations in temperature substantially beyond the temperatures within the two rooms 1, 2. Also, the thickness of such a belt may be approximately .006. Preferably, the upper runs or flights of the conveyors are supported on relatively closed spaced rollers 3S (FIG. 2) that may also be carried bythe frameV supporting the belts, and the middle belt 34 is offset to the left, as viewed in FIG. 2, a suicient distance so that material deposited on the upper flight of the upper conveyor 33 at the right hand end of the latter will be discharged onto the left hand end of the middle conveyor 34, upon movement of the upper Hight of said upper conveyor to the left, or in a direction away from the discharge end of the feed conveyor 37. Rollers 39 may support the lower flight of each conveyor against sagging. p

Also, the lower conveyor 35 is offset to the right, as seen in FIG. 2, relative to the middle conveyor 34, so that material discharged from the right hand end of the middle conveyor will be carried on the latter to the left.

The movement of the upper ight of conveyor 33 is away from the discharge end of the feed conveyor or from right to left as seen in FIG. 1. The movement of the upper flight of the middle conveyor 34 is from left to right, as seen in FIG. 2, while the movement of the upper ight of the lower conveyor is from the right to the left.

The pulley shafts at the left hand ends of the conveyors 33, 34 and 34, 35, carry pulleys over which a pair of crossed belts 40, 41 extend for simultaneous movement of belts 33, 34 to the left, as seen in FIG. 2, and for movement of the belt 32 to the right, all at the same rate of speed since the pulleys mounting belts 33-35 are the same diameter. A pulley on the conveyor shaft at the left hand end of the lower conveyor 35 is connected by a belt 42 with a motor 43 for so simultaneously moving said conveyor belts 33-35.

In the above structure alternate ends of the conveyors 33-35 are the discharge ends, with the discharge ends of the upper conveyor and the lower conveyors being at their left ends, as seen in FIG. 2, and with the right hand end of the middle conveyor being its discharge end. The ends of the conveyor -32 opposite to their discharge ends may be called their receiving ends.

A scraper 44 (FIG. 3) similar to a doctor, extends across and substantially in sliding engagement with the outer surface of each of the conveyors 33-35 at the clischarge end of the latter, each scraper being formed with an edge positioned adjacent to the belt and an upper surface 45 over which the material on the belt is adapted to be carried away from the belt for dropping against the concave surface of a downwardly extending guide plate 46 that, in turn, will deliver the material onto the receiving end of the conveyor therebelow in an inverted position. A spring 47 may connect each scraper with the conveyor supporting frame to yieldably urge each scraper into engagement with the outer or load supporting surface of each conveyor where `the latter extends around the pulley, so that the pulley will constitute a rigid backing for the conveyor belt, and each guide plate 46 may be also supported on the conveyor frame. Each scraper or doctor 44 is of a plastic or of any other suitable material that will not injure the Teflon of the belt engaged thereby.

The discharge end of the lower conveyor is adjacent to partition 3, and is adapted to discharge the material thereon, onto the lower end of an endless elevator conveyor 50 that slantingly extends upwardly from below the discharge end of conveyor 35 through partition 3 and into the upper end portion of the subliming room. Slats or equivalent conventional load carrying supports on the elevator conveyor 50 will thus receive the material from the discharge end of the lower-conveyor 9 and will carry it upwardly through the partiton 3 for discharge into the subliming room 2 at the upper end of the latter adjacent to the upper end of Wall 3.

Also carried by any suitable frame means in the freezing room 1 in a position over each conveyor 33-35 is a horizontally elongated air discharge nozzle 52 preferably of the width of each conveyor and extending from end to end thereof. The lower side of each nozzle is provided with downwardly directed relatively closely spaced discharge openings for discharging air uniformly against any product supported on the upper flight of each conveyor. In fact the lower side of each nozzle is a perforated plate. The body of each nozzle above the discharge opening is preferably of progressively decreasing cross sectional area transversely of the length thereof in directions away from the central portion of the nozzle body so as to provide for said uniform discharge of air over and against substantially the entire upper surface of each of the conveyors 33-35.

Conduits 30, 31 and 32 (FIG. 1) extend respectively from the plenum chamber 18 to the enlarged central portion of each of the nozzles 51 for supplying air to each of the nozzles under pressure from the" blowers of the air conditioning units 4, 5. The provision of the two air cooling or air refrigeration units 4, '5 enables a continuous discharge of cold air from nozzles 51 onto the products on conveyor belts 33-35. The fan motors for the fans in units 4, 5, are schematically indicated at 53, 54 in FIG. l, and the solenoid valves in the spray lines 14, 15 leading to units 4, 5 are indicated at 55, 56, all being in the circuit in which timer 26 is positioned. The high torque damper motors 24, 25 are, as already explained, also in this circuit.

The timer control automatically alternately actuates the fan motors for periods of, say, twelve minutes, as an example. When the fan rnotor 53 in unit 4 is actuated the damper motor *24 will automatically move dampers y22 to open position and motor 25 will automatically close the damper 23 and the solenoid valve 56 will be actuated to open the spray line 15 for defrosting the coils in unit 5. Solenoid valve 55 will be closed. At the end of the twelve minute period the timer 26 will break the circuit to fan motor 53 and close it to fan motor 54 and the damper motor 24 will close the damper 22 and motor 25 will be actuated to open damper 23, while the solenoid valve 56 will be closed and the valve 55 will be opened to defrost the coils in unit 4.

It should be noted that the timer is preferably adjusted to permit adequate time for `draining the water from the drain pan in each unit 4, 5 before the fan motor in each cooling unit is started.

Substantially the same conveyor and nozzle arrangement is provided within the sublimation room 2 as in the freezing room 1, there being a plural-ity of endless, horizontally extending, vertically spaced, parallel superposed conveyors 59, 60, '61 within room 2, and over each conveyor is a downwardly directed air discharge nozzle 62, that corresponds in structure to each nozzle 52. Each nozzle 62 is disposed over the upper llight of each of the conveyors l59-61 in the same manner as nozzles 52 are disposed over conveyors 33-35.

The conveyors 59-61 may be offset relat-ive to each other in the same manner as the conveyors 33-35 so that the discharge end of the elevator conveyor will discharge the material therein onto the receiving end of the upper conveyor 59, and the discharge end of the lower conveyor 61, which is at the left hand end as seen in FIG. 2, will discharge the material therein onto the receiving end portion of a discharge conveyor 63. The discharge conveyor is horizontally elongated,.and extends through an opening in the end wall 64 of the housing, for carrying the material discharged thereon out of the sublimation room 2.

Any suitable frame may support the conveyors 59-61 and nozzles 62, and any other parts associated with said conveyors, within the sublimation room.

A motor 66 may be connected by any suitable driving connection with the conveyors 59-61 for moving the latter in directions corresponding to the directions of movement of the correspondingly positioned conveyors 33-35 in the freezing chamber 1. A crossed belt 67 may connect the pulleys on the shafts at the left hand ends of conveyors 59, 60 and a crossed belt 68 may connect the pulleys at the left hand ends of conveyors 60, 61 for simultaneously moving the conveyors I59-61 for carrying products back and forth within the chamber 2 and for nally discharging the products onto the receiving end of discharge conveyor 63.

Rollers `69 support the upper runs or flights of conveyors 59-61 and rollers 70 below the lower runs of the conveyors support the belts against sagging. Scrapers '71 corresponding to scrapers 44 are at the discharge ends of conveyors 59-61, while guide plates 72 guide the material on the conveyors 59-61 from the discharge ends of the upper conveyors onto the receiving ends of the lower conveyors. Sideplates 7'3 on the guide plates, as well as sideplates '74 along opposite edges 4of the upper rims of each of the conveyors will prevent material from 4falling off the conveyors.

An important feature is the fact that the product being frozen, if in a slurry, will be broken up, upon being removed by the doctor 44 at the discharge end of each conveyor, and the guide plates 46, 72 will invert the pieces. However, by the time the product reaches the lower end of the elevator conveyor 50 in room 1 it will usually be in a more or less granular form, and moisture within the pieces or objects will be in ice crystals concentrated at the outer surfaces of `the pieces. By breaking up the slurry in room 1 into small pieces, the moisture is completely frozen before it reaches conveyor 50, and the ice crystals are not so deep as to fail to be completely s-ublimed in room 2.

Heretofore, Where the product is not so broken or inverted, many hours are required to effect the desired freezing. In the present instance, the particles or discrete objects are again inverted or are changed in their positions upon discharge at the discharge ends of the conveyors, in the sublimation chamber.

An essential feature of the present invention is that the vapor pressure of the air ejected against the objects on the conveyors 33-35 must be less than the vapor pressure of the ice crystals at the surfaces of such objects or particles. The vapor pressure of the ice crystals of say 0.18 and of 0.10 of dry air, or air containing substantially no more than 15 grains of moisture per pound, blown against the ice would effect the sublimation of the ice and complete sublimation of the ice crystals would occur, in the present example, in approximately one hour, or a total of approximately two hours would be required, instead of a total of approximately 24 to 26 hours for the same products or objects by the conventional methods, and in vacuum systems.

It is to be understood that the number of conveyors, rates of speed of the conveyors, and other details are not necessarily to be considered as being restrictive of the invention, but are by way of illustration.

The method itself may be ydescribed as being one in which the material to be frozen is conducted along a path of travel in direct heat transfer relation to cold air at approximately 15 F. to 30 F. until substantially all the moisture within such material is in frozen crystals at the surface of said material, and changing the surfaces of said material in said direct contact with said air at intervals during movement of said material along said path of travel, and thereafter removing said material from the influence of said cold air and moving said material along a second path of travel. During movement along said second path, the material is subjected virtually continuously to contact with dry air having a lesser vapor pressure than said ice crystals, whereby said ice will sublime, and changing the surfaces so contacted during said movement of said material along said second path. This movement along said second path is continued until Vall the ice is sublimed, leaving the material dry.

The feature of breaking the material into discrete particles during movement of the material along the first path is obviously a feature where the material is a slurry, and even where the material, such as string beans, for example, is frozen it will be broken up, since beans, sliced onions etc., will be frozen together.

Preferably Vconstant speed motors are used to drive the conveyors and the drive pulley on each motor may be changed to vary the speed of the conveyors. Also, control may be had by changing the temperature of the drying air to be ejected from nozzles 36 in combination with a change in the speed of the the conveyors.

The employment of thin, Teflon belts 33-35 and 59-61 is highly desirable, since these belts do not stretch and have good heat transfer characteristics, and are very strong. Also they are impervious to moisture and are unaffected by acids, oils, etc. present in fruits, vegetables, and most products.

It is to be understood that the time cycle for freezing and defrosting may vary, but the time switch is adjusted so that a continuous ow of freezing air is ejected from the nozzles 52 onto the products on the conveyors.

The air in room 1 will enter air inlets in the lower portions of the` air cooling units 4, 5 for circulation across the coils in said units 4, 5 and back onto the products on conveyors 33-35.

The cooling units, the dampers, timer switch, damper motors, drainage system for the defrosting water, etc. are all conventional, the damper motors 24, 25 being high torque, unidirectional, two-position, power units used for damper controls, each including a built-in limit switch for stopping the crank arm connected with the damper louvers, in positions 180 apart.

In the ducts 30, 31, 32 that carry the cold air from the plenum 18 to the nozzles 52, each duct has a locking type balancing damper therein. These are independently, manually adjusted and locked in adjusted positions. Thus, when desired, the air flow to the nozzles may be varied to suit conditions. For example, it may be found desirable to increase the air flow to the upper nozzle 52 and then to balance the air flow in the lower two ducts relative to each other. Obviously, any desired variation can be made.

In each dehumidifier unit provision may be made for precooling the air that enters the dehumidifiers for drying therein, and for final ejection into the drying room. In the system disclosed, and as described in my copending application, Serial No. 197,298, filed May 24, 1962 and entitled Dehumidifier and Method, the dry air is normally discharged from the dehumidifier for conduction to the drying room at a relatively low temperature.

Separate air ducts 77, 78, 79 connect at one of their ends with the central portions of nozzles 62 and the other ends of said conduits may connect with the dry air outlets of separate air dehumidifiers 80, each of which continuously produces dry air, and each of which is preferably of the type disclosed in my above-mentioned copending application. A suction blower 81 in each conduit 77-79 draws atmospheric air through each dehumidifier 80 and discharges it through the nozzles 62 and onto the products on the belts 59-61.

The dehumidifiers 80 are outside the sublimation room as are the blowers 62, and the air ejected from each nozzle is preferably approximately air containing 15 grains of moisture per pound at an elevated temperature of approximately 110 F.-120 F. An air exhaust fan 82 communicates with the upper portion of the sublimation room to provide positive removal of the vapor laden a1r.

From the foregoing illustration it is seen that where each of the three conveyors in the freezing room and in the sublimation room, respectively, is of substantially the same length, or approximately thirty feet, the three conveyors in each room have substantially the same capacity as a single conveyor that is substantially feet ong.

The rate of travel of the load carrying flight of each conveyor 33-35 and 59-61 is preferably approximately 0.66 feet per minute, or a total of one hour in the freezing room and one hour in the sublimation room.

During the time the product is carried through the freezing room, it is subjected to air from nozzles 52 at a temperature of approximately -15 F. to 30 F.

Automatic take up means, such as indicated generally at 83 in FIG. 4,may be provided for the top belts 33 and 59 in the freezing and drying rooms to keep these belts taut, since the material fed onto the top belt 33 may be relatively warm, or may come directly from a cooker, while the material fed onto the top belt 59 in the drying room will be quite cold, having come directly from the freezing room. Obviously, automatic or other take up means may also be provided for the other belt in the freezing and drying rooms, if desired.

I claim:

1. Apparatus for freeze-drying a product comprising,

in combination:

(a) conveyor means for supporting said product thereon for substantially continuous movement from a receiving station to a discharge station;

(b) a cold air discharge nozzle over said conveyor means and directed toward the latter for discharging air against a product supported on said conveyor means during movement thereof away from said receiving station; and air cooling means connected therewith for supplying cold air to said cold air discharge nozzle;

(c) a dry air discharge nozzle over said conveyor means between `said cold air discharge nozzle and said discharge station directed toward said conveyor means for discharging dry air against a product supported on said conveyor means during movement thereof toward said discharge station;

(d) said conveyor means being horizontally elongated and said air discharge nozzles being also horizontally elongated longitudinally of the conveyor means therebetween for respectively discharging cold and dry air against said product over a relatively long period of time during movement of said product from said receiving station to said discharge station,

(e) air cooling means being adapted to cool air for discharge from the latter at a temperature of substantially F. to -20 F.;

(f) air drying means communicating with said dry air discharge nozzle for drying air to the content of approximately 15 grains of moisture per pound at said discharge nozzle, and

(g) separate means for discharging said cold and said dry air from said air cooling means and from said air drying means and out of said cold air nozzle and said dry air nozzle and against a product in said conveyor means with substantial force and for a suflciently extended period to completely freeze moisture in such product by said cold air and to substantially completely sublime the moisture so frozen by said dry air;

(h) a freezing room within which said cold air discharge nozzles and the portion of said conveyor means toward which they are directed are positioned;

(i) a drying room adjoining said freezing room including a partition wall common to both said freezing room and said drying room;

(j) an opening formed in said partition wall and a portion of said conveyor means extending through said opening conveying said product from said freezing room to said drying room;

(k) the portions of said conveyor means within said freezing room and said drying room respectively, extending backward and forwardly from an elevated point at said receiving station to a lower point at a level substantially below said elevated point, at said discharge station to thereby effect a freezing and drying of said product within a relatively short distance in a horizontally extending direction.

2. Freeze-drying apparatus comprising:

(a) a freezing room;

(b) a drying room adjacent to said freezing room,

(c) an upper, intermediate end lower endless, horizontally extending, horizontally elongated conveyor within said freezing room in parallel, spaced, superposed relation,

(d) a first, second and third endless, horizontally extending, horizontally elongated conveyor within said drying room in parallel, spaced, superposed relation with said first conveyor uppermost and said second conveyor therebelow and said third conveyor lowermost;

(e) the said conveyors within said freezing room and said drying room each having an upper horizontally disposed flight adapted to support material thereon,

(f) feed means at one end portion of said upper conveyor for feeding material to be frozen thereon and (g) material conveying transfer means at the one end of said lower conveyor that is opposite to the end therof corresponding to said one end portion for receiving material discharged from said one end of said lower conveyor,

(h) conveyor actuating means operatively connected with said conveyors that are within said freezing chamber for moving the upper flights of said upper conveyor away from said feed means and for moving said lower flight toward said material conveying means and for moving the upper flight of said intermediate conveyor in a direction opposite to the direction of movement of the upper flights of said upper and lower conveyors,

(i) separate means for guiding material discharged from said upper conveyor at the end of the latter opposite to said feed end onto the end portion of the upper flight of said intermediate conveyor that is adjacent thereto and for guiding the material discharged from the intermediate conveyor at the end thereof opposite to said end lportion of the upper flight of the latter onto the end portion of the upper flight of the lower conveyor that is adjacent thereto for movement of said material on said last mentioned flight to one end of said lower conveyor for discharge onto said material conveying transfer means,

(j) said material conveying transfer means extending from said one end of said lower conveyor to a position over one end of said first conveyor and being adapted to carry material discharged thereon from said lower conveyor to said one end of said first conveyor for discharge onto said first conveyor at said one end of the latter,

(k) said conveyors within said drying room having upper horizontally extending flights for supporting said material thereon for movement in directions longitudinally of said flights upon actuating said last mentioned conveyors,

(l) conveyor actuating means operatively connected with said first, second and third conveyors for moving the upper flights of said first and third conveyors in the same direction away from said material conveyor transfer means and for moving the upper flight of said second conveyor in the opposite direction,

(rn) separate means for guiding material discharged from said fruit conveyor at the end thereof that is opposite to said transfer means onto the end portion of said second conveyor that is adjacent thereto and for guiding the material discharged from the end of said second conveyor that is oppositeto said end portion of the latter onto the end portion of the upper flight of said third conveyor that is adjacent thereto for movement of the material on said third conveyor to and for discharge from the end that is opposite to said end portion of the upper flight of the latter;

(n) means at said last mentioned end of said third conveyor for receiving the material discharged therefrom and for conducting it out of said drying room,

(o) air discharge nozzles over and directed downwardly onto the upper flights of the conveyors within said freezing and drying rooms,

(p) means for supplying air at approximately l5 to -30 temperature under pressure to the nozzles Within said freezing room for discharge onto material on said upper flights of the conveyors in said freezing room,

(q) means for supplying dry air containing substantially no more than 15 grains of moisture per pound of air, under pressure, to the said nozzles within said drying room for discharge of said air onto the material on the upper ights of the conveyors in said drying room.

3. The method of drying a slurry that comprises the steps of (a) moving a layer of slurry along a predetermined path of travel;

(b) progressively freezing the moisture in said slurry during said movement;

(c) inverting the material of said slurry during said movement at a point in said path after a substantial References Cited by the Examiner amount of the moisture has been frozen but before all of said moisture has been frozen, and then con- UNITED STATES PATENTS tinuing the movement of said slurry during freezing 1,748,043 8/ 1927 Grupe 62-74 of the moisture therein until substantially all of said 2,254,420 9/1941 Cleveland 62-380 moisture has been frozen; 2,467,318 4/1949 Kellogg 34-5 X (d) the said freezing of said moisture being effected 2 284 848 6/1942 Ryan 34 5 gy blowing atmospheric 5air at a temperature of 2435503 2/1948 Levinson 34 5 rom approximately -1 F. to approximate y -30 F. downwardly against said layer whereby 2452983 11/1948 Blrdseye 34- 203 said air will be blown -directly against opposite sur- 2483254 9/1949 Aimy 34-5 faces of said layer in succession to freeze said mois- 2,523,552 9/1950 Blrqseye 34"5 X ture at the opposite surfaces of said layer in the 2,533,125 12/1950 LeVlllSOIl 34-5 form of ice crystals at said surfaces; 2,668,364 2/ 1954 Colton 34-5 (e) after substantially all of the moisture in said slurry 2,751,687 6/ 1956 Colton 34-5 has been frozen, continuing the movement of said 2,896,425 7 /1959 Dunbar 62 40g X frozen slurry along a second path of travel and at 2,967,405 1/1961 Taylor 62 408 X the same time blowing air containing no more mois- 3,096,163 7 /1963 Merryman 34 5 ture than substantially 15 grains per pound of said air at approximately F. to 120 F. against said ice crystals until said ice crystals have been completely sublimed.

ROBERT A. OLEARY, Primary Examiner. NORMAN YUDKOFF, Examiner. 

3. THE METHOD OF DRYING A SLURRY THAT COMPRISE THE STEPS OF: (A) MOVING A LAYER OF SLURRY ALONG A PREDETERMINED PATH OF TRAVEL; (B) PROGRESSIVELY FREEZING THE MOISTURE IN SAID SLURRY DURING SAID MOVEMENT; (C) INVERTING THE MATERIAL OF SAID SLURRY DURING SAID MOVEMENT AT A POINT IN SAID PATH AFTER A SUBSTANTIAL AMOUNT OF THE MOISTURE HAS BEEN FROZEN BUT BEFORE ALL OF SAID MOISTURE HAS BEEN FROZEN, AND THEN CONTINUING THE MOVEMENT OF SAID SLURRY DURING FREEZING OF THE MOISTURE THEREIN UNTIL SUBSTANTIALLY ALL OF SAID MOISTURE HAS BEEN FROZEN; (D) THE SAID FREEZING OF SAID MOISTURE BEING EFFECTED BY BLOWING ATMOSPHERIC AIR AT A TEMPERATURE OF FROM APPROXIMATELY -- 15*F. TO APPROXIMATELY -30*F. DOWNWARDLY AGAINS SAID LAYER WHEREBY 